U.S. Pat. No. 5,125,463 describes one of the most recent designs for adjustable bent subs. This design incorporates a single bend in the device, with the bend occurring between end faces of a housing and a sliding ring axially slidable on a mandrel. The housing has an inner shoulder. The mandrel extends into the housing and is capped with a locking cap whose end face abuts the inner shoulder of the housing. Tightening of a locking ring forces the locking cap against the inner shoulder of the housing and the sliding ring against the end face of the housing. The faces formed by the end face of the sliding ring, end face of the housing, inner shoulder and end face of the locking cap are all offset from a central axis of the device so that rotation of the parts in relation to each other results in a bend in the device.
While this design has proved useful, the tool is somewhat difficult to adjust and improper adjustment may result in an alignment problem that could lead to failure of the tool. The present invention provides an improvement on this prior art design that makes proper adjustment easier to achieve.
There is therefore provided in accordance with one aspect of the invention, an adjustable bent housing for use in downhole drilling which includes a housing, mandrel, ring and locking mechanism. The housing has a housing central axis, a downward facing end face defining a plane whose normal is offset from the housing central axis, and an inner shoulder parallel to the downward facing end face. The mandrel has a mandrel central axis, a first end dimensioned to fit inside the housing and having a downward facing outer shoulder defining a plane whose normal is offset from the mandrel central axis. The ring is axially slidable on the mandrel, with a ring central axis and an upward facing end face defining a plane whose normal is offset from the ring central axis. A locking mechanism, preferably a mandrel head threaded onto the mandrel, engages and disengages the upward facing end face of the ring with the downward facing end face of the housing and simultaneously engages and disengages the inner shoulder of the housing with the outer shoulder of the mandrel.
Keys or like means are preferably used to control the position of the ring on the mandrel in selected circumferential positions only. One of the keys may be differently sized from other keys to assure proper alignment. Preferably markings on the ring and housing are used indicate relative degrees of rotation of the housing in relation to the ring.